Process for the treatment of molten metals

ABSTRACT

The invention relates to a process for the treatment of molten metals with reactive additives whereby the reactive additive is added into the molten metal at a point between the pouring of the molten metal from the melting container and the entry of the molten metal into a casting mould. The additive is contained within a reaction chamber positioned between the ladle and the mould the demensions of the chamber being such that there is always adequate molten metal present in the chamber to cover the additive.

United States Patent [191 McCaulay et a1.

PROCESS FOR THE TREATMENT or MOLTEN METALS Inventors: James Lindsay McCaulay; Clifford Matthew Dunks, both of Reigate, England Materials and Methods limited, Surrey, England 1 Filed: Mar. 13, 1970 Appl. No.: 19,404

Assignee:

Foreign Application Priority Data Mar. 13, 1969 Great Britain 13289/69 US. Cl. 75/130 R, 75/130 B, 164/55 Int. Cl. C22c 37/00, B22d 27/18 Field of Search 75/130 AB, 130 B, 130 C,

References Cited UNITED STATES PATENTS June 25, 1974 3,306,737 2/1967 Muhlberger 75/130 AB X 3,328,164 6/1967 Muhlberger 75/130 AB X 3,666,449 5/1972 Alt 75/130 B 3,703,922 11/1972 Dunks & McCaulay 75/130 B FOREIGN PATENTS OR APPLIGATIONS 702,776 l/l954 Great Britain 75/130 R 972,708 10/1964 Great Britain 75/130 R 1,132,055 10/1968 Great Britain 1,132,056 10/1968 Great Britain 75/130 R Primary ExaminerL. Dewayne Rutledge Assistant Examiner--Peter D. Rosenberg Attorney, Agent, or Firm-Plumley & Tyner [57] ABSTRACT 8 Claims, 1 Drawing Figure PAIENTEDJUNZSIHH 3.819.365

' INVENTORS JAMES LINDSAY MCRULAY BY CLIFFORD MATTHEW DUNKS ATTORNEY 1 PROCESS FOR THE TREATMENT OF MOLTEN METALS This invention relates to an improved process for the treatment of molten metals. 7

Many methods have been evolved for introducing alloys or compounds in the treatment of molten metals to improve ormodify their properties. All such techniques have been aimed at improving reliability of the treatment and/or "improving the process efficacy.

Where highly reactive metals, alloys or compounds are to be introduced to molten metals acute processing problems are often encountered which adversely effect reliability leading to inadequate treatment and subsequently a sub-standard end product.

Such conditions prevail in the manufacture of the socalled nodular orspheroidal graphite cast irons. As is well known, these irons are produced by treating a base cast iron composition with suitable nodularisers such as the metals, alloys, or compounds of Mg, Ca, Na, Li, Sr, Ba, Ce, Di, La and Yt. These treatment materials are either readily oxidisable at the temperature of the molten cast iron or are volatile and hence, present difficulties in obtaining reliable recoveries and are often characterised bylow recoveries which inevitably leads to excessive processing and uncertain final results costs.

Many processes have been devised to introduce these nodularising materials to molten cast iron, some using 'theassistance of gas agitation, some relying on plunging the nodulariserinto the molten cast iron while other utilise sub-surface injection techniques introducing the nodulariser via a graphite or refractory lance. All of these processes suffer certain limitations in that in someinstances reliability of treatment is'poor and this leads to a natural tendency to over-treatment.

Apart from the unnecessary alloy costs involved,

I these nodulariser materials are also carbide stabilisers risers are expensive. Further the excessive quantities of nodularising alloys tends to give rise to the formation of oxides or silicates which become entrapped in the melt producing dirtycastings or dross defects. Also they form sub-surface blow holes and elephant skin and intensify shrinkage of the molten iron during solidification giving rise to shrinkage and other defects causing loss of both physical properties and confidence in the finished product. I

According to this present invention, it is now possible to overcome most of these problems and atthe same time reduce the cost of manufacture. This has been achieved by effecting the nodulariser addition within a pre-formed cavity either in the furnace spout, or laundeer or dependant on production circumstances incorporated within a separate treatment device. This pre- I formed cavity into which the nodulariser is placed may be termed the reaction chamber.

Accordingly, the present invention provides a process for the introduction of a reactive additive'into a molten metal wherein the additive is contained in a reaction chamber through which the molten metal is chamber is filled to an extent caused to flow, the dimensions of the chamber and the flow rate of the molten metal through the chamber being so correlated that sufficient molten metal is always present in the chamber at least to cover the additive. g The invention also provides apparatus comprising a vessel for the molten metal to be treated, an outlet from the vessel for the molten metal, means for directing a flow of molten metal to a desired location and, between the vessel and said desired location a reaction chamber adapted to receive a reactive additive and positioned and dimensioned so that metal from the vessel flows through the chamber at such a rate as to ensure that the to cover any additive contained therein.

The chamber is constructed with a suitable inlet for the incoming metal and an outlet orifice of such a dimension that will ensure that the nodulariser in the reaction chamber is completely covered with metal almost immediately. In .certain instances it may be preferable to have a removable plug in the outlet orifice to allow the reactionv chamber to fill, after which the plug is withdrawn. The supply of molten metal to the reaction chamber must be such as to maintain the chamber full, or at least the nodulariser covered with metal, during processing.

The reaction chamber may be constructed of any refractory material or fabricated in metal lined with refractory material.

When the molten metal comes into contact with the nodulariser the reaction commences uniformly. The reaction continues progressively until all the nodulariser has been dissolved. Due to the fact that the reaction commences immediately the molten metal covers the nodulariser, solution occurs out of contact with air,

hence volatilisation and oxidation are completely eliminated during processing. In some cases it may be advantageous to provide a gas-tight cover for the reaction chamber and an inlet for inert gas so that an inert atmosphere can be maintained in the chamber. Further the usual pyrotechnics, fume, and metal splashing which normally accompanies the introduction of nodularisers is also eliminated, probably due in part to the solution occurring in the absence of air and in part to the solution occurring gradually as the molten metal runs across the nodulariser, thus giving controlled solution. Hence it is now possible accurately to control the precise amount of additive which is required to improve the physical properties and change the base microstructure. This then eliminates the previous danger due to dross inclusions and over-treatment.

For example we have achieved complete conversion of the graphite form from flake to perfect spheroidal shape with as little as 0.15 percent of the nodulariser .alloy used in accordance with the invention. With any of the conventional techniques previously employed, it would have been necessary to use at least 0.5 percent 'of the same additive.

In this process, any of the well-known nodularising metals, alloys, compounds or mixtures thereof may be The apparatus according to the invention is illustrated in the accompanying drawings.

In the drawings is illustrated the means for directing the flow of metal from the vessel, not shown, to the desired location for the metal, also not shown.

Referring now to the drawing molten metal from the vessel enters a pouring zone 1 which acts as a header. Metal leaves the pouring zone by way of a metal inlet 2 and passes into a passage 3 leading to the reaction chamber 4. The reaction chamber is provided with a cover 5. Molten metal leaves the reaction chamber 4 after, having been in contact with additive in the chamber by way of metal outlet 6 from which it passes to spout 7 from which it is directed to the desired location.

The following Examples serve to illustrate this aspect of the invention:

Example 1.

In this case, the reaction chamber was constructed as an integral part of a cupola launder. The quantity of nodulariser reagent (consisting of 55 percent Si, percent Mg and the balance Fe) was calculated based on 0.35 percent of one-ton molten cast iron, i.e., 7.84 lbs. of nodularising reagent was used, in this instance in the form of h inch X A inch lumps.

The nodulariser was charged into the reaction chamber and the replaceable lid secured. The cupola taphole was opened and the molten metal flowed into the chamber via the inlet orifice. The exit orifice had been plugged and immediately it was clear that an adequate head of metal had formed within the chamber, this plug was removed and treated metal flowed from the exit orifice the remainder of the distance from the launder into the collection ladle placed below. In this treatment, the dimension of inlet and outlet orifice of the reaction chamber were directly related to the metal flow rate from the cupola such that a constant head of metal was maintained within the reaction chamber during tapping.

Subsequent examination and testing of the treated iron showed that all the graphite had been converted to the nodular form and that the casting properties had been improved from a nominal tons per square inch tensile strength base metal to 49.7 tons per square inch tensile, with an elongation of 5 percent.

Example 2.

The supply of molten metal was from a 3000 kg capacity mains frequently furnace. The reaction chamber was constructed within a separate device fabricated with mild steel plate and lined with a refractory material. The device may be described as a short secondary launder mounted on four leg supports. The moulded lining formed a pouring basin to receive the molten metal from the melting furnace and this basin then channelled into the inlet orifice of the reaction chamber. The outlet from the reaction chamber connected with a preformed down-tube to direct the treated metal into a collection ladle located directly below. 7.5 kg of a nodularising mixture consisting of percent metallic magnesium, 50 percent calcium silicide, and 20 percent ferro silicon was placed in the reaction chamber and the replaceable lid secured.

The molten cast iron from the furnace was then poured into the basin formed in the secondary launder device and flowed into the reaction chamber. The pouring rate was controlled to ensure that the chamber was maintained full during processing. Solution and treatment progressed as described in Example 1.

Examination of the treated metal confirmed that all the graphite had been converted to a spheroidal form. The resultant properties were 34 tons per square inch tensile strength and 19 percent elongation the matrix structure in this case being largely ferritic determined by the composition of the base charge in relation to the casting section size.

The residual magnesium content of the treated metal was 0.048 percent equivalent to a recovery of 96 percent.

In the course of developing the concept of this invention, it has been found advantageous in certain circum stances to utilise carbonaceous bearing refractory to form the reaction chamber, thus providing a reducing atmosphere within the chamber. Also, use can readily be made of an inert or reducing gas to evacuate the air from the chamber prior to and during processing, the said gas being conveniently introduced through a jet or porous membrane located in the replaceable lid construction. Another procedure is to place a small quantity of a suitable reagent which will decompose readily in contact with molten metal and provide an inert or reducing atmosphere. For example, carbonates, solid hydrocarbons pitch and coal tar. These variations are an insurance against oxidation of the nodulariser, especially helpful where difficulties are encountered in maintaining the nodulariser adequately covered by molten iron.

The invention has been described above with particular reference to nodularisation of cast irons but the concept of this invention is also adaptable for the efficient introduction of any metal, alloy, or compounds into a molten metal. Most advantage is gained where the additive to be introduced is highly reactive at the temperature of the molten metal or even at the other extreme where it is difficult to dissolve or where problems are encountered in obtaining uniform solution and homogenity in the treated metal when using conventional techniques.

We claim:

1. A process for the introduction of a reactive additive into molten metal prior to being cast in a mold, which comprises passing the untreated molten metal in a flowing stream through a bed of granular reactive additive contained in a reaction chamber separate from the mold in which the treated molten metal is later cast, the size of said bed of additive and the flow rate of said molten metal through the bed being so correlated that the bed is always covered with molten metal and that substantially every portion of the molten metal contacts said additive.

2. A process as claimed in claim 1 wherein the flow of molten metal is initially prevented from leaving the reaction chamber to establish a depth of metal adequate to cover the additive and the metal is then allowed to flow through the chamber at a rate to ensure that the additive remains covered.

3. A process as claimed in claim 1 wherein the metal is iron and the reactive additive is a nodularising agent.

4. A process as claimed in claim 3 wherein the nodularising agent is used in an amount of from 0.15 to 0.5 percent by weight based on the weight of the molten metal.

and the launder through which the molten metal flows.

8. A process as claimed in claim 1 wherein the reaction chamber is provided with a substantially gas-tight cover and a gas inlet so that a non-oxidising atmosphere can be maintained in the reaction chamber. 

2. A process as claimed in claim 1 wherein the flow of molten metal is initially prevented from leaving the reaction chamber to establish a depth of metal adequate to cover the additive and the metal is then allowed to flow through the chamber at a rate to ensure that the additive remains covered.
 3. A process as claimed in claim 1 wherein the metal is iron and the reactive additive is a nodularising agent.
 4. A process as claimed in claim 3 wherein the nodularising agent is used in an amount of from 0.15 to 0.5 percent by weight based on the weight of the molten metal.
 5. A process as claimed in claim 1 wherein the reaction chamber is an integral part of a cupola launder.
 6. A process as claimed in claim 1 wherein the reaction chamber is situated in the pouring spout of the vessel containing said untreated molten metal.
 7. A process as claimed in claim 1 wherein the reaction chamber forms part of a treatment device separate from the vessel containing said untreated molten metal and the launder through which the molten metal flows.
 8. A process as claimed in claim 1 wherein the reaction chamber is provided with a substantially gas-tight cover and a gas inlet so that a non-oxidising atmosphere can be maintained in the reaction chamber. 